package com.xtwy.basealgorithm.base58;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;

public class Base58 {

	public static final char[] ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".toCharArray();
	private static final int[] INDEXES = new int[128];

	static {
		for (int i = 0; i < Base58.INDEXES.length; i++) {
			Base58.INDEXES[i] = -1;
		}
		for (int i = 0; i < Base58.ALPHABET.length; i++) {
			Base58.INDEXES[Base58.ALPHABET[i]] = i;
		}
	}

	/**
	 * Encodes the given bytes in base58. No checksum is appended.
	 */
	public static String encode(byte[] input) {
		try {
			return Base58.encode(input, "US-ASCII");
		} catch (UnsupportedEncodingException e) {
			throw new RuntimeException(e); // Cannot happen.
		}
	}

	public static String encode(byte[] input, String charsetName) throws UnsupportedEncodingException {
		if (input.length == 0) {
			return "";
		}
		input = Base58.copyOfRange(input, 0, input.length);
		// Count leading zeroes.
		int zeroCount = 0;
		while ((zeroCount < input.length) && (input[zeroCount] == 0)) {
			++zeroCount;
		}
		// The actual encoding.
		byte[] temp = new byte[input.length * 2];
		int j = temp.length;

		int startAt = zeroCount;
		while (startAt < input.length) {
			byte mod = Base58.divmod58(input, startAt);
			if (input[startAt] == 0) {
				++startAt;
			}
			temp[--j] = (byte) Base58.ALPHABET[mod];
		}

		// Strip extra '1' if there are some after decoding.
		while ((j < temp.length) && (temp[j] == Base58.ALPHABET[0])) {
			++j;
		}
		// Add as many leading '1' as there were leading zeros.
		while (--zeroCount >= 0) {
			temp[--j] = (byte) Base58.ALPHABET[0];
		}

		byte[] output = Base58.copyOfRange(temp, j, temp.length);
		return new String(output, charsetName);

	}

	public static byte[] decode(String input) throws IllegalArgumentException {
		if (input.length() == 0) {
			return new byte[0];
		}
		byte[] input58 = new byte[input.length()];
		// Transform the String to a base58 byte sequence
		for (int i = 0; i < input.length(); ++i) {
			char c = input.charAt(i);

			int digit58 = -1;
			if ((c >= 0) && (c < 128)) {
				digit58 = Base58.INDEXES[c];
			}
			if (digit58 < 0) {
				throw new IllegalArgumentException("Illegal character " + c + " at " + i);
			}

			input58[i] = (byte) digit58;
		}
		// Count leading zeroes
		int zeroCount = 0;
		while ((zeroCount < input58.length) && (input58[zeroCount] == 0)) {
			++zeroCount;
		}
		// The encoding
		byte[] temp = new byte[input.length()];
		int j = temp.length;

		int startAt = zeroCount;
		while (startAt < input58.length) {
			byte mod = Base58.divmod256(input58, startAt);
			if (input58[startAt] == 0) {
				++startAt;
			}

			temp[--j] = mod;
		}
		// Do no add extra leading zeroes, move j to first non null byte.
		while ((j < temp.length) && (temp[j] == 0)) {
			++j;
		}

		return Base58.copyOfRange(temp, j - zeroCount, temp.length);
	}

	public static BigInteger decodeToBigInteger(String input) throws IllegalArgumentException {
		return new BigInteger(1, Base58.decode(input));
	}

	//
	// number -> number / 58, returns number % 58
	//
	private static byte divmod58(byte[] number, int startAt) {
		int remainder = 0;
		for (int i = startAt; i < number.length; i++) {
			int digit256 = number[i] & 0xFF;
			int temp = (remainder * 256) + digit256;

			number[i] = (byte) (temp / 58);

			remainder = temp % 58;
		}

		return (byte) remainder;
	}

	//
	// number -> number / 256, returns number % 256
	//
	private static byte divmod256(byte[] number58, int startAt) {
		int remainder = 0;
		for (int i = startAt; i < number58.length; i++) {
			int digit58 = number58[i] & 0xFF;
			int temp = (remainder * 58) + digit58;

			number58[i] = (byte) (temp / 256);

			remainder = temp % 256;
		}

		return (byte) remainder;
	}

	private static byte[] copyOfRange(byte[] source, int from, int to) {
		byte[] range = new byte[to - from];
		System.arraycopy(source, from, range, 0, range.length);

		return range;
	}

}
